HTTPS simply uses a symmetric key to encrypt all the application data

TLS1.2 uses cert on the web server back to the client so that the client will encrypt his premaster symmetric key with the Public Key. And send it back to the webserver. And webserver will obtain the symmetric key with his private key. And start the encryption of data and sending it to client. Two rounds trip.

TLS1.3 where the client and web server both have a private key and using the Diffie Hellman method to exchange the symmetric key.

Client will encrypt the his key a with public key g. And the webserver will encrypt its private key b with g. So now we have ag and bg. Now sending client the bg and now client combined three keys . Will now be abg. And same to the webserver.

Then the key exchange is done.